2021: four-year old season
On April 4, Contrail started the season off with the Grade I Ōsaka Hai. In that race, he was the most favored to win, with his opponents including the likes of Gran Alegria, who won the JRA Award for Best Sprinter or Miler the previous year but never ran a race of medium distance up until that point; Salios, whom Contrail had beaten twice before; and the undefeated Lei Papale, who was running a Grade I race for the first time. However, the race, which was held on a soft track due to the rain, saw Contrail struggle to catch up from the mid-field position; before ultimately finishing third behind Lei Papale and Mozu Bello.
After the Ōsaka Hai, the horse was initially planned to race the Takarazuka Kinen, only to skip the race to head to the Autumn Tennō Shō later that year as the horse's condition was not sufficiently recovering.
On October 31, Contrail was entered to contest the Autumn Tennō Shō held at Tokyo Racecourse. In that race, he was unable to make a good start, having to pace behind Gran Alegria and Efforia for most of the race. On the final stretch, Contrail managed to pass Gran Alegria, but failed to catch up to Efforia, who won by a length against Contrail.
On November 28, Contrail was entered to run the Japan Cup once again, this time having been announced prior that the horse would retire after this race. The race saw four Tokyo Yushun winners enter the race for the first time, Contrail, Makahiki, Wagnerian, and Shahryar; who was that year's Derby winner that beat Efforia in that race. During the race, Aristoteles was the front runner while Contrail ran in the middle of the pack, before Kiseki took over the lead at the third corner. Kiseki came in the final stretch with a four length lead but Authority, Shahryar, and Contrail closed in before Contrail took over the lead, finishing his final race with a two length lead.
Following the Japan Cup, a retirement ceremony for the horse was held at the parade ring of the Tokyo Racecourse. During the ceremony, Fukunaga thanked the horse, saying "I believe that we were able to achieve the Triple Crown with the breeder, trainer, and jockey forming a trinity; and the fact that Contrail was able to accomplish that makes him such a talented horse. As a jockey, I was able to experience something that a horse man could hardly achieve. That I am very grateful for. I also believe that Contrail is the only horse that can continue the trend of 'an undefeated Triple Crown winner born out of another undefeated Triple Crown winner', and I hope that some day this horse could send such a horse to the tracks." Meanwhile, Yahagi commented "It was a battle against pressure, but it was a fun two years. This is the first time I rode the horse myself, but it felt as if I was flying. I believe his offsprings will do so too. I'd like to win the Prix de l'Arc de Triomphe with one of his progenies some day."
In January 2022, Contrail was awarded the JRA Award for Best Older Male Horse, although he lost the Japanese Horse of the Year to Efforia. In addition, Contrail was given a rating of 126 and ranked fifth in the 2021 World's Best Racehorse Rankings, while the JRA gave the same rating on their JPN Thoroughbred Ranking, with Contrail given the highest rating of all older horses.
Contrail was inducted into the Japan Racing Association Hall of Fame in 2024.
